1. Field of the Invention
The present invention relates to an aircraft wing, aircraft wing composite material, and method of manufacture thereof. More particularly the present invention relates to an aircraft wing which has both high bending flexibility in the wing chord direction and high load bearing capacity and high capacity to maintain the wing shape in the wing span direction, and to which morphing aircraft technology can be applied in the high-speed regime where aerodynamic forces are high. The present invention also relates to an aircraft wing composite material and method of manufacture thereof.
2. Description of the Related Art
Research and development into technology, in which the shape of wings can be changed arbitrarily to improve the flight performance and characteristics of aircraft just like birds (hereinafter referred to as “morphing aircraft technology”), is being carried out mainly in the USA. Aircraft wings to which morphing aircraft technology can be applied require both high bending flexibility in the wing chord direction and high capacity to maintain the wing shape in the wing span direction.
In the prior art, in order to provide high bending flexibility in the wing chord direction and high capacity to maintain the wing shape in the wing span direction, air-filled wings are known (for example, JPO's patent Publication No: H11-512998). These wings include an external part with an upper skin and lower skin formed from an airtight woven substrate material, and an internal part with woven webs formed from an airtight woven substrate material. A plurality of void cells are formed in the upper and lower skins and the woven webs. Supplying compressed air to or reducing compressed air from the void cells can change both the wing height and shape or, air storage channels with airtightness are formed in the upper and lower skins and the woven webs, and supplying compressed air to or reducing compressed air from the air storage channels can change both the wing height and shape.
Also, air-filled wings made from a rubber material, in which pipes are passed through the inside and the internal pressure in the wing can be adjusted to change the cross-sectional shape of the wing by supplying compressed air to or reducing compressed air from the inside through the pipes, are known.
Furthermore, wings made from shape memory alloys or piezoelectric materials capable of changing their shape and angle are known.
In the above-mentioned air-filled wings, bending flexibility can be ensured in the wing chord direction by adjusting the pressure of the air filling the wing. However, air is a compressible fluid, so the wing span direction will also have bending flexibility in the same way. Therefore, high bending flexibility in the wing chord direction together with high capacity to maintain the wing shape in the wing span direction is not achieved. The other wings also do not achieve high bending flexibility in the wing chord direction together with high capacity to maintain the wing shape in the wing span direction as in the case of the air-filled wings.
From a viewpoint of achieving both high bending flexibility in the wing chord direction together with high capacity to maintain the wing shape in the wing span direction, it is easy for those skilled in the art to conceive of a wing made from an anisotropic composite such as carbon fiber-reinforced plastic (hereafter referred to as “CFRP”) instead of the above woven substrate or rubber material. In other words, in a wing made from carbon fiber-reinforced plastic with the carbon fiber aligned unidirectionally in the wing span direction, the bending stiffness in the wing span direction (Ds) is high due to the strength anisotropy of the carbon fiber, and the bending stiffness in the chord direction perpendicular to the wing span direction (Dc) is lower.
However, in the above wing made from CFRP, if the stiffness in the wing span direction is increased, the stiffness in the chord direction also increases. On the contrary if the stiffness in the wing chord direction is reduced, the stiffness in the wing span direction is also reduced. As a result, the optimum stiffness ratio (Dc:Ds) is 1:15 at most, which is insufficient for application to a wing for morphing aircraft technology where the stiffness requirement is Dc:Ds=1:100 or greater. At the stiffness level, the strength in the wing chord direction is also insufficient for the application of morphing aircraft technology.
Also, it is easy for those skilled in the art to conceive of a wing made from a rubber material reinforced in one direction, for example carbon fiber-reinforced rubber (CFRR), instead of a plastic material reinforced in one direction. In other words, in a wing made from carbon fiber-reinforced rubber with the carbon fiber aligned unidirectionally in the wing span direction, the stiffness increases in the wing span direction due to the strength anisotropy of the carbon fiber, while the stiffness in the wing chord direction reduces due to the elastic action of the rubber. As a result, it is possible to achieve stiffness ratios of 1:100 or greater.
However, in unidirectionally reinforced rubber materials the compressive strength of the wing is low in the fiber direction, in other words, the wing span direction. Therefore, there is a problem of loss of load bearing capacity in the above wings made from CFRR due to bending forces caused by aerodynamic forces in the high-speed regime where aerodynamic forces are high.